(1) Field of the Invention
The present invention relates to a route computing system, and more particularly to a route computing system for computing a route based on routing protocol packets.
(2) Description of the Related Art
In recent years, IP-VPN (Internet Protocol-Virtual Private Network) services using the Internet have been in widespread usage as means for performing communications between divisions of enterprises, instead of conventional WANs (Wide Area Networks) using dedicated lines. IP-VPNs are realized by routers that are designed based on protocols such as OSPF (Open Shortest Path First), BGP (Border Gateway Protocol), and MPLS (Multiprotocol Label Switching). As the Internet has become more and more popular, there are growing demands for IDCs (Internet Date Centers). An IDC provides a service for connecting servers entrusted by a plurality of customers to a router for connection to the Internet and maintaining the servers.
Routers for carriers and enterprises are equipped with a forwarding engine having a CAM (Content Addressable Memory) as a hardware piece, for example, for searching for the destination route of a packet with a full-wire transfer capability in order to transfer the packet at a high speed. The destination of a packet is determined by the hardware-implemented forwarding engine, and the packet is transferred with a full-wire transfer capability. When a network route is changed due to an exchange of route information, the construction of a route database, a circuit fault, or the breakdown of another router, the route database is not recomputed by a forwarding engine, but by a dedicated protocol processor.
The number of Internet routes is growing year after year, making the Internet topology more complex. When a certain node is down, a large number of route changes occur. The period of time required to compute a new bypass route until communications are recovered is governed by the performance of the protocol processor of a router, and may sometimes reach several tens of seconds. Therefore, the protocol processor is required to be of high performance.
There is known a router which is capable of transferring data even when their route computer for computing routes suffer a failure (see, for example, Japanese Unexamined patent publication No. 2002-164913 (paragraphs [0018] and [0019], FIG. 2)). The router has a route computer and a responder for returning a Hello packet, the responder being separate from the route computer. In the event of a failure of the route computer, the responder continuously operates to exchange a Hello packet.
Another known router has a dedicated module for performing a forwarding process and a routing process. The module has a specially designed process of controlling a connection to a bus for reducing a reduction in a transfer capability when a plurality of modules are connected (see, for example, Japanese Unexamined patent publication No. 10-301910 (paragraphs [0035] through [0040], FIG. 1)).
Still another router has route computers for computing routes, associated with respective interfaces, so that route computations are distributed for making themselves higher in speed (see, for example, Japanese Unexamined patent publication No. 2003-8627 (paragraphs [0022] through [0024], FIG. 1)).
The built-in protocol processor of a router is difficult to replace itself alone. If it is to be replaced with a higher-performance protocol processor, then it is necessary to redesign and manufacture a hardware system including the processor, and hence the replacement is costly. Particularly, route computations performed by a router need to be processed at a high speed in order to shorten a communication cutoff time upon a route change. However, since route changes do not occur frequently, it is of little merit against an investment cost to redesign a hardware arrangement including a router processor for replacement.